1. Technical Field of the Invention
The present invention relates to an image forming device such as copier, facsimile machine, and printer, and more particularly, to a cleaning process in an image forming method for recording images by ejecting toners onto a recording member.
2. Description of Related Art
As the capacity of personal computers has been increased in recent years, a great mass of documents are now handled in offices. Also, in accordance with the progress in network technologies, printers and copiers of high processing ability have come into wide use. Meanwhile, the recent trend is towards color documents with the rapid spread of ink jet printers or the like. However, an image forming device that is capable of outputting satisfying monotone images as well as color documents at high speed is still being developed and realization of such device is awaited. Below, explanation is made with reference to figures showing prior art image forming devices.
FIG. 7 is a schematic illustration showing the construction of an electric signal recording method disclosed in Japanese Published Examined Patent Application 44-26333. Reference numerals 71, 72, 73, 74, 75, 76, 77 in the figure respectively represent a backside electrode, recording medium, control grid, mesh electrode, toners, brush, and power supply. Toners 75 are tribo-electrically charged to acquire, for example, negative charges by rotation of the brush 76. Between the mesh electrode 74 and backside electrode 71 is connected the power supply 77 for creating an electric field by which charged toners 75 are accelerated towards the recording medium 72. By providing electric signals 78 across the mesh electrode 74 and control grid 73, the amount of toners passing through the mesh electrode 74 and the position of toners adhering on the recording medium 72 can be controlled in accordance with the polarity and strength of the inputted signals. Specifically, when "on" signal as the electric signal 78 is inputted to the control grid 73 (which means that positive polarity is given in the case of toners 75 having negative charges), the gate is opened, whereupon toners 75 travel in the parallel electric field formed between the mesh electrode 74 and backside electrode 71 by means of the power supply 77 in the direction of recording medium 72. Conversely, when "off" signal as the electric signal 78 is inputted (which means that negative polarity is given in the case of toners 75 having negative charges), the gate is closed and toners cannot pass through the control electrode 73. In this way, an image is recorded by the combination of electric signals "on" and "off".
FIG. 8 is a schematic illustration showing the construction of another prior art image recording device disclosed in Japanese Published Unexamined Patent Application 58-104769. In FIG. 8, signal electrodes 101, base electrodes 103, and insulating members 102 interposed therebetween, are disposed such as to surround an aperture (gate) 104. Reference numeral 105 is a recording member, and 106 is a backside electrode that is connected to a source of direct current voltage 109 and a voltage of about 300V is impressed thereto. 107 is a toner conveying member, 108 is a source of alternating current voltage, 110 is a signal power supply, that is connected to the signal electrodes 101 and base electrodes 103 for impressing a voltage of 50V thereto for recording. 111 is a mono-component insulating magnetic toner powder, 112 is a fixed magnet, and 114 is a magnetic blade.
Next, actions of this image recording device will be explained. A thin layer of mono-component insulating magnetic toner powder 111 is formed on the toner conveying member 107 by means of the magnetic blade 114. Alternating current, either solely or overlapped with a direct current, is applied across the base electrodes 103 and toner conveying member 107, as a result of which the mono-component insulating magnetic toners 111 begin a reciprocating motion. Then, recording signals are inputted to the signal electrodes 101 and a voltage of forward polarity is applied thereto, upon which the mono-component insulating magnetic toners 111 pass through the aperture 104, travel along the electric field created by the backside electrode 106, and adhere to the recording member thereby accomplishing image formation. Conversely, when no voltage is applied to the signal electrodes 101, or, in case that a voltage of opposite polarity is applied thereto, the mono-component insulating magnetic toners 111 do not pass through the aperture 104 and image formation is not performed. In the arrangement shown in FIG. 8, a high voltage is impressed to the backside electrode 106 during the non-image formation period, thereby causing toners which remain in the aperture to eject; it is thus prevented that the aperture becomes clogged up with toners.
Above described conventional image forming devices are, however, subjected to the following problems.
(1) In the method disclosed in Japanese Published Examined Patent Application 44-26333 wherein the gate to the parallel electric field formed between the mesh electrode and backside electrode is opened and closed by means of electric signals inputted to the control grid, the mesh electrode and control grid must be sufficiently distanced with each other, so that open/close signals generated by the control grid are effected without failure. If the mesh electrode and control grid were to be disposed in the vicinity or in contact with each other, electric signals would have to have a great voltage differential, which would necessitate the use of switching elements of high voltage, leading to increase in size of the device itself and in cost. On the contrary, if the spacing between the mesh electrode and control grid is too great, because controllability of flying toners will decrease, and even the basic performance required for the device such as forming favorable images can hardly be achieved.
(2) In the system where signal electrodes and base electrodes are formed on both sides of insulating members as set forth in Japanese Published Unexamined Patent Application 58-104769, lines of electric force along which toners are ejected are intensively formed between the signal electrodes and base electrodes, wherefore toners tend to stick to the wall surface of the aperture and the aperture is easily clogged up with toners.
(3) As a countermeasure for this, a high voltage electric field is created across the signal electrodes and backside electrode. However, application of a high voltage in the area where electrodes are adjacent with each other causes serious problems such as discharge destruction and damage to the signal electrodes, whereby reliability is considerably decreased.